1. Field of the Invention
This invention relates to color inkjet recording films, and, more particularly, to color-receptive films coated with copolymers of vinyl caprolactam and dimethylaminopropyl methyl acrylamide having excellent color stability towards light.
2. Description of the Prior Art
The advent of color inkjet printing has been instrumental in fueling the print-on-demand revolution and has also created a number of challenges. Often, the surface of the desired media does not possess the necessary properties for accepting the inkjet ink. This results in long dry times and/or a poor ink-jet image. It has long been recognized that a surface treatment or media coating plays a critical role in the final print quality. Numerous media coatings are known in the art. They may contain any number of components and often consist of more than one layer. These ink-receptive coatings generally contain at least one hydrophilic polymer; often poly(vinylpyrrolidone) (PVP). PVP brings many benefits to properly formulated media coatings including rapid ink dry time, excellent print quality, highly resolved circular dots, and high, uniform optical density. Furthermore, copolymers of vinylpyrrolidone (VP) along with other suitable comonomers, such as dimethylaminoethyl methacrylate, acrylic acid, or vinyl acetate, have been used separately or in conjunction with PVP, to further optimize performance. Unfortunately, ink-jet images printed on VP-based formulations are prone to fading with exposure to light. Increasing demands for achievable ink-jet images has created a need for polymers with all the positive attributes of vinyl pyrrolidone and with improved light stability.
Accordingly, the object of the invention is to provide a clear, white-appearance, water-resistant, color inkjet-receptive film coated with a polymer which provides the color image thereon with excellent, long-term color stability.
What is described herein is a clear white-appearance, water-resistant, color ink-receptive film having a copolymer of (a) vinyl caprolactam and (b) dimethylaminopropyl methacrylamide coated thereon; preferably the weight ratio of (a):(b) is 50-95:50-5; optimally about 80:20. The ink-receptive film of the invention is capable of being printed from a color inkjet printer to form color images thereon which exhibit excellent long-term color stability towards light. These advantageous results are achieved herein while retaining the desired properties of rapid ink dry time, good print quality, highly resolved circular dots, and high, uniform optical density, characteristic of other systems.
Test Methods
Coating formulations were prepared by dissolving the test copolymer in a suitable solvent at 10 wt.%. Drawdowns were cast on a polyester substrate using a #38 Mayer bar and allowed to dry overnight under ambient conditions to give a dry coating thickness of xcx9c9 micron.
Coated samples were then printed using a selected printer. Individual blocks of cyan(C), magenta(M), yellow(Y), and black(K), approximately 1xe2x80x3 X 1.75xe2x80x3 in size, were printed side by side. Small blocks of C, M, Y, and K, approximately xe2x85x9xe2x80x3xc3x97xc2xcxe2x80x3, are printed repeatedly down one edge of the page to provide a built-in time-line for measuring off-set time as described below.
Optical density (OD) was determined on blocks of cyan(C), magenta(M), yellow(Y), and black(K) using a Macbeth Densitometer. A large value for optical density is preferred.
Off-set time is the minimum time required for no ink to transfer to a cover sheet placed on top of the print when contacted with a 4-lb. Roller immediately after printing. Ink transfer is determined at the point where the OD after testing dropped by a value of 0.2 units. Fast off-set times are most desirable.
Light fastness is determined by measuring the change in optical density after 21 hours exposure to either a QUV or Atlas weatherometer. The results are given as a % change in optical density.